New York add soil

I have a working slinky loop system with a flow center. It is a McQuay unit that I believe is designed to shut down when the EWT goes below 30 degrees. When the outdoor temperature gets below 20 degrees I add heat to supplement as that seems to be the temp where it is needed. The loop is buried 6-7'. I was thinking of adding 1' of soil over the entire footprint of the slinky loop field to keep the EWT a bit higher. Is this worth the effort?

 

Do you have antifreeze in the loop? From what I have read all units have the ability to go below 30*F. On the control board there is a jumper that needs to be cut to allow the unit to operate below freezing.

 

heat pumps with closed ground loop systems are rated by AHRI for heating at EWT of 32F. I can't imagine a situation where your unit could be rated for heating at 32F EWT but wouldn't work at 30F EWT (unit probably doesn't even know the difference). A quick google search pulls up specs for McQuay units with heating output numbers at 20F EWT so it seems like it is definitely doable. I don't know the specifics of your McQuay unit (see ChrisJ above re jumpers) or if you have antifreeze in your loop (you need it) but the only reason supplemental heat would come on in the situation you are describing is because the unit is too small for the heating load and can't keep up. Is this a single stage unit? Single stage units are typically sized for cooling in a heating dominated climate with supplemental heat picking up the load during the extreme cold temps. Adding dirt over the loop would do nothing in that situation as the loop isn't the issue. Units are sized for peak demand (coldest/warmest days of year). ground loop is sized for total BTUs pulled out of ground/pushed into ground on a yearly basis.

 

Thanks Chris...yes the loop has antifreeze. After having the geo shut down twice during the winter, which was right about at the 30 degree EWT, I called a tech in the spring. He checked the antifreeze level. It seems like it was good to 24 degrees. He suggested adding 20 more gallons of antifreeze which of course dropped the freeze point but I am travelling at the moment and do not have that number in front of me. There are 4- 1" slinky loops at about 750' each. The next winter it shut down again at the 30 degree EWT again. From that time on, during extreme cold, we have started adding heat with an insert fireplace and gas space heaters to keep above that 30 degree EWT. When I get home this weekend I could post a pic of the control board if that would be of help.

 

Thanks...this is a single stage unit. We have been very pleased with the performance of this unit except for the shut down issue and we only need to deal with that a few weeks a year. I was just thinking maybe another 1' of soil over the loop fields making them 7-8' deep instead of 6-7' deep might be helpful. If you don't think it would be beneficial that would save me a lot of work. I have a feeling and hope that there might be that jumper that is the culprit.

 

I've had my system 8 years. When we had polar vortex year, I was pushing 26-29 degrees for a couple weeks straight, but it kept going. I have freeze protection to 18 degrees.

Yes another foot of dirt would help. How much is not certain, but all is better. One thing to consider is lawn mowing. I always try and ensure I don't clip too closely near end of season so I have more of a bed of lawn. It can serve as a great insulator from the cold of winter.

 

Thanks for your response. I never thought about lawn mowing....sure would not hurt to leave it long. Maybe leave the leaves on until spring as well. Thanks for the input.

 

if your EWT is 30F when your unit needs supplemental heat, you don't have a loop problem. heat pumps are rated to provide heat at that EWT temp-just look up the unit specs online. Adding soil (or not mowing) or whatever other step you do to provide an incremental amount of soil over the loop is a waste of time and money. My 400ft deep wells have the EWT approach 30F in the middle of winter too and my units don't stop providing heat (because they were sized for heat load). You would need to add many many feet of soil over the loops to get the EWT up. Replace the unit with a larger tonnage if you want heat from it all winter without elec supplemental heat. The unit can't keep up with the load which is why it needs supplemental heat. If your EWT was 20F (or lower) when it stopped providing heat, then you would have a loop issue. Unit is sized for the instantaneous load and responds to air temp fluctuations. Loop is sized for the yearly load and couldn't care less if the outside temp drops to 20 for a week

 

Thankjs... I agree with you on the loop...it should be sufficient for the application. But there seems to be an automatic shutdown of the geo at 30 degrees EWT. Just trying to figure that out.

 

Unit can't keep up with thermostat set point so it turns on supplemental heat. As an experiment, turn the thermostat down and see if the supplemental heat still comes on when outside air temp drops into range that supplemental heat typically turns on.

 

Or jumper/unit configuration that ChrisJ alluded to. Can't help on that one. I do know that some units can be configured for an open loop system with higher EWTs. If configured in that manner, it would turn on the elec heat sooner. But your description doesn't seem to fit that. It sounds more like unit capacity gets maxed out

 

Thanks...There is no automatic electric backup coil ... heat is supplemented from gas space heaters and a wood fireplace insert that we use when the EWT gets too low. Still thinking it might be that jumper issue.

 

Hi and welcome!
If the unit shuts off at the ewt of 30 you have a unit control issue. I have a leaky house on a closed loop. My unit will run non stop and not meet demand. It does not shut down, it just can not keep up. I am with Chris on this one, check unit set up configuration on the control board.
Hope this helps
Eric

 

That is good to read...I don't mind the not catching up but shutting down at 0 degrees is problematic especially when we am not at home during that time.

 

As we get into spring, I note how dramatically my grass is reemerging only in areas that had solid leaf cover. That slight bit of insulation is dramatic for soil temperature impact.

 

I can't think of any way that lawn mowing would have a significant effect on the performance of a properly designed closed loop field.

 

I don't expect it could have a significant impact on a properly designed field. On a marginal design, it could add a bit of benefit. Dense vegetative and snow cover insulate the soil and reduce the rate of soil freezing and thawing. I think the key word here is dense. I'd be curious to know how much, but if you ever note where the moles and mice live in landscapes, it is the thick native grasses or under leaf piles or mulch where soil temps are much more temperate in winter.

I don't have substantive data to show improvements in my system, but I did add a foot of dirt in many areas. In other areas, I am encouraging existing bamboo forest to extend over some loop areas and in others, I have probably added two feet of mulch, just because one of the local tree services wanted a dump site for tree chipper debris. None of this was intended to improve geothermal performance, but primarily focused on leveling some washed out areas and increasing my usable yard and enhancing landscapes while preventing further washouts. Anecdotally, it seems I get through winter with more constant loop temps, but I know well that the plural of anecdote doesn't equal data. Take it with a grain of salt. I did study agriculture and soil science for two years and note that winter ground cover substantially improves soil health due to increased microbiome in areas just below the frost depth at a lesser penetration.

 

So the loop is now protected to more like 15*F?

I believe this is how units are delivered, which is for open loop, the jumper is cut to allow the loop temp to go below 30*F.

I read through 2 different McQuay manuals, couldn't find a reference to cutting the jumper. Maybe contact McQuay or Ingrams to see if someone knows how to configure unit for closed loop.

 

I looked at several manuals also. Nothing about setting jumpers for closed vs. open loop or for pure water vs. antifreeze. In the Enfinity manual, McQuay references two separate units--a "standard range" unit with minimum EWT of 55 deg and an "extended range" with minimum EWT of 20 deg, so it might not be configurable.

In the Enfinity manual there is mention of a (apparently optional) BACnet control module with configurable water limits.

• Attained Temperature and Water Temperature Alarms –Attained temperature, water temperature alarms with software-adjustable setpoints are available in software. The controller samples supply air and records attained temperatures for heating and cooling. If after two hours of operation, the attained temperature does not meet the software-configurable setpoint for heating or cooling as appropriate, a software alarm occurs. The alarm automatically resets when the attained temperature is within setpoints. The controller also monitors leaving water temperature. If the leaving water temperature is outside software-configurable setpoints, compressor operation is suspended and high or low water temperature alarms occur. The alarm automatically resets when the water temperature returns to within 6 deg. F of the setpoint.

As stated, the OP needs to determine the capabilities of his particular model number. Maybe he has, or can add, the BACnet controller.

If the EWT is 30 and lockouts occur, it seems possible the problem could be insufficient flow rate. Maybe increasing the flow rate would raise the LWT enough to avoid the lockout?

 

Thanks for all the input. I have been on the road for the last week so just getting a chance to respond.
I did a freeze test on the glycol with these results: at 24* starting to thicken ...20* heavy liquid...18* light slush...14* heavy slush.
Reading in the manual I noticed the following:

Vertical (Floor) Water Source Heat Pumps Sizes 009-070 (3/4 to 6 Tons)
 Model VFC (Standard Range: 55°F to 110°F)
 Model VFW (Geothermal Range: 30°F to 110°F)

This unit is a 4 ton VFW model. Notice the geothermal range above suggests 30 may be the low range.
Attached I hope you find a picture of the board. Not sure if is of any help. I can take another if it would be helpful.
I did talk to Ed at Ingram at one point and he thought it should work down to 24*. In my notes he said "AP3 jumper should be factory connected freeze protection" (page 28 in his manual).